This invention relates to an improvement in feed control mechanisms for the work feed systems of sewing machines. Such work feed systems are generally of the drop feed type (known also as fourmotion feeds) where a work engaging feed dog is elevated into work engagement during the feed advancement or reverse stroke and drop out of work engagement during the return stroke, such as disclosed in the U.S. Pat. No. 3,527,183 issued Sept. 8, 1970.
This patent also discloses the manner in which the feed regulating or rock shaft is connected to the work engaging feed dog. As disclosed, the feed regulating or rock shaft is provided with a feed block in which is formed a guide slot. A slide block is positioned to ride within the slot and, in cooperation with a feed advance eccentric mounted on the bed shaft, controls the incremental advance of the feed dog during the work feed stroke. Rotation of the rock shaft determines the angular position of the guide slot and thus the extent of the linear work feed motion transmitted to the feed dog in either forward or reverse feed motion at a selected stitch length. A feed control system for regulating the position of the rock shaft as shown and claimed in the U.S. Pat. No. 3,834,334.
The present invention is specifically directed to improving such feed control mechanisms by providing an automatic means which temporarily reverses the direction of stitching movement for a predetermined number of stitches, i.e. back-tacks, along the stitching path. Such a back-tack may be required for example, at the start and finish of a line of stitching to provide a secure anchorage and prevent the pulling apart of the layers of fabric which may be stitched together.